The present disclosure relates to a light-emitting diode (LED) device, and in particular, to an LED device, which has a structure of transparent metal oxide/metal/transparent metal oxide for enhancing light extraction efficiency and current injection efficiency, and which is provided with current injection electrodes for increasing current injection efficiency.
Electron-hole recombination may occur at a junction region of p- and n-type semiconductor materials, when an electric current is provided to the junction region. A light emitting diode (LED) is a semiconductor device that is configured to generate light using such electron-hole recombination.
The LED device, which is one of III-V nitride-based semiconductor devices, has been evolved from a lateral structure to a flip-chip or vertical structure allowing for a high brightness property. Especially, in the field of vehicle lighting, the vertical LED device has been actively developed to realize a high brightness property under high-power and high-temperature environment.
For the lateral and vertical LED devices, in order to improve the light extraction efficiency, there have been many studies on material and structure of a device or electrode.
GaN-based LED devices may be classified into three types: (a) top-emission type, (b) flip-chip type, and (c) vertical type. In all of the LED devices, some characteristics (e.g., low contact resistance, uniform current spreading, efficient thermal emission property, and high light extraction efficiency) are required, regardless of their types and structures.
According to a conductivity type of a semiconductor material, a material, which has an increased carrier concentration or has a work function higher or lower than that of the semiconductor material, may be used for electrodes of an LED device. In this case, it may be possible to lower a Schottky barrier at an interface between the semiconductor material and the electrode or to reduce a width of a depletion area.
In the case of the top-emission or vertical type LED device, photons produced in an active layer should be emitted to the outside of the device through a current spreading layer thereon. Current spreading, transparency, and current injection efficiency are parameters directly affecting performance of such LED devices. Accordingly, it is necessary to increase optical transmittance and electric conductivity of an upper electrode, in a p- or n-type GaN semiconductor device.
Conventionally, the upper electrode may be formed using a process for forming an electrode pad, on which a wire bonding process will be performed. However, the upper electrode may be provided in the form of a grid or comb. The upper electrode may be formed of at least one of opaque metallic materials (e.g., Cr, Al, Ni, or Au), thereby reducing light extraction efficiency.
According to some embodiments of the inventive concept, an upper electrode pad and an upper electrode may be formed to be spaced apart from each other, and the electrode and current spreading layer or the electrode itself may be formed to have a structure of highly transparent metal oxide/metal/metal oxide. This may make it possible to improve light extraction efficiency of the LED device
According to some embodiments of the inventive concept, a transparent upper electrode and a plurality of dot-shaped upper current injection electrodes may be used to improve light extraction efficiency and current injection efficiency of an LED device.